Actuating device for loud speakers



C. L. FARRAND ET AL ACTUATING DEVICE FOR LOUD SPEAKERS Filed Oct. 1926 mwll hum".

44;, 4 INVENTORJ 4% W ATTOR NEYS Patented Feb. 14, 1928.

UNITED STATES PATENT OFFICE.

CLAIR L. FARRAND, OF FOREST HILLS, NEW YORK, AND ERNEST ROSS. OF EAST ORANGE, NEW JERSEY; SAID ROSS ASSIGNOR T0 FARRAND MFG. CO. INC., OF LONG ISLANDCITY. NEW YORK, A CORPORATION OF NEW JERSEY.

ACTUATING DEVICE FOR LOUD SPEAKERS.

Application filed October 18, 1926. Serial No. 142,186.

This invention relates to electromagnetic actuating devices for loud speakers.

One object of the invention is to provide an electroma netic actuating device in which the pole pieces are associated with the polar portions of the permanent magnet in an improved manner. I

Another-object of the invention is to provide an electromagnetic actuating device'in which the speech coils are associated with the remaining parts of the device in an improved manner and are held in place by simple but effective means.

A further object of the invention is to provide improved means for adjusting the size of the air gap between the poles of the pole pieces.

An actuating device constructed in accordance with the invention is illustrated in the accompanying drawings in which Fig. 1 is a side elevation of the actuating I device;

Fig. 2 is a top plan view of the same;

Fig. 3 is a horizontal section taken on the line 33 of Fig. 1;

Fig. 4 is a vertical transverse section taken on the line 4-4 of Fig. 3;

Fig. 5 is a perspective view showing one of the pole pieces and the clamp for attaching it to the polar portion of the permanent magnet;

Fig. (i is a horizontal section taken on the line ti-6 of Fig. 1;

Fig. 7 is a side elevation of the actuating device as viewed from the right in Fig. 1;

and

Fig. 8 is a perspective view of one of the speech coils. g

The particular actuating device shown in the drawings was designed for use in a loud speaker having a large conical diaphragm made of paper. However, it may be used for actuating diaphragms of other types such as flat diaphragms, curved diaphragn'is, etc. and, therefore, no particular form of. diaphragm has been illustrated in the drawings.

The improved actuating device comprises a permanent horseshoe magnet 1 one leg of which may be fastened to a supporting plate 2 by means of screws 3, washers or spacers 4 of non-magnetic material preferably being interposed between the magnet and the plate.

The plate 2 constitutes means for attaching the magnet to upright posts 5 forming a part ofthe framework of the loud speaker. The remaining portions of the loud speaker itself are not illustrated as they form no part of the present invention. A pole piece 6 is secured to the inner face of each leg of the magnet 1. As best shown in Figs. 2, 3 and 5 each pole piece is substantially U-shaped or in other words forms one-half. of a hollow rectangle. pieces are preferably laminated and made of some magnetic material. Each lateral face of the base portion of each pole piece has riveted thereto a strip 7 of non-magnetic material such as copper, brass or bronze and the ends of these strips project slightly beyond the sides of the pole pieces as indicated at 8 in Fig. 5. Each pole piece is clamped to the inner face of one of the legs of the magnet 1 by means of a clamp 9 of copper, brass, bronze or the like. The clamp 9 is in the center of a U-shaped' strap which is adapted to partly encircle a leg of the mag net. Each leg of the clamp has a portion of reduced width 10 adapted to engage between the two adjacent projecting ends 8 of the strips 7 in such a way that when the clamp is retracted shoulders 11 on the clamp pull back against the projecting ends 8 of the strips 7 and pull the pole piece into ongagement with the leg of the magnet. Set screws 12 associated with the clamp engage with that i'ace'ot'the leg of the magnet which is opposite the pole piece in order to retract the base of the pole piece against the magnet. Each pole piece 6 is associated with the polar portion of one leg of the magnet and they are so positioned that they lie substantially in .the same plane and project toward each other as shown in Fig. 3 to form a rectangular opening. However, the adjacent ends of the pole pieces do not meet but are spaced apart slightly to form one pair of poles 13 and a second pair of poles 14. An armature 15 is mounted between the pole pieces in such a way that-one end of the armature lies between the poles 13 and the other end of the armature lies between the poles 14. The armature is yieldingly held in its central position bymeans of a flat spring lti which extends vertically above and below the plane of the pole pieces. At

The pole I nut 31.

flanges. 23-: and 24.

its upper end the spring is fastened by means of a screw v16' to a post 17 preferably of non-magnetic material which is se cured to one-leg of the magnet 1. One of the screws 3 which serves to attach the magnet-to the plate 2 may be utilized for holding the post 17 in place. The lower endbe wound on a bobbin or spool-like structure which comprises a hollow core 22 and end The core 22 and the flanges 2324 may be made' of mica, celluloid, or the like. The spring 16 for the armature passes between the two coils and in order to hold the coil spools apart to make room for the spring they may be separated by spacers 25 made of mica. celluloid or the like. The .two speech coils are connected with each other and to the leads in the usual manner. he flanges 23 and 2-l of the coil spOOlS are notched as shown at 26 and these notches receive the bases of the pole'pieces so that the coil spools or bobbins are eflectivcly locked in place;

One end of the farmature 15 has soldered theretoa rod 27 which is connected at its outer end to the end of a flat spring 28 as best shown in Figs. 1, 2 and 7. The other end of the flat spring 28 is clamped to the outer face of the outer magnet leg by means of a screw 29 and nut 31. The screw 29 is rigidly secured at its inner end to the post 19. If desired the screw 29 may he rigidly attached to the post 19 as by means of a pin 30 as shown 'in Fig. (3. The screw 29 passes loosely through the leg of the magnet and through the spring 28 and is provided at its outer end with the clamp A spacing block or washer 32 is preferably positioned at either side of the spring 28 and the screw 29 also passes loosel v through these washers. Just .to the inside of the leg of the magnet through which the screw 29 passes the screw is provided with an adjustable stop nut 33. It will now be obvious that byntightening the nut 31 the outer leg of the magnet is forced into en- 'gagemcnt with the stop nut 33. the magnet or at least one leg thereof being sufiiciently resilient to allow this action to take place. \Vhen .the stop nut 33 is moved inwardly the nut 31 can'be further tightened t.ll(.l(l'l moving the outer leg of the magnet-further inwardly and thereby shortening the air gaps between the two pairs of poles of the pole pieces The nut 33 constitutes a stop It will be noted that one' for limiting the' inward movement of the leg of the magnet and, therefore, determines the ultimate adjustment of the air gap.

A rod 3t is soldered to the spring 28 preferably at a point which lies between the rod 27 and the screw 29 and this rod. extends outwardly to a point where it may be conveniently attached to the diaphragm not shown in the drawing. v

The electromagnetic actuating device-described above operates in a well known manner, that is, when the speech currents pass through the coils-20 and 21 they act upon the coaxial armature and vary the attraction between the ends of the armature and the pole pieces so that the armature vibrates in exact accordance with variations in the speech current and the vibrations of the armature are transmitted through the rod 2?, spring :18 and rod 3% to the diaphragm of the loud speaker.

it will now be seen that each pole piece is attached to a leg of the magnet by a clamp which at least partly encircles the magnet leg. The clamp is wholly external with respect to the magnet leg, that is, it affords means for attaching the pole piece to the magnet leg without drilling the magnet, without the aid of screws which screw into the material of the magnet and without the g5 aid of any device which would necessitate the performance of any drilling or other similar operation upon the magnet. The bases of the pole pieces are fiat and are drawn into tight engagement with the corresponding faces of the magnet by the screws 1; so that a good magnetic contact is obtained between the pole piece and the polarportions of the magnet. It will also be noted that the speech coils including their spools or bobbins are conveniently housedwithin the rectangular opening formed by the two pole piccr-s. The notches formed in the end flanges of the coil spools constitute. simple but ctl'i-clivc means for holding the speech 11 coils in place. The air gap is adjusted in a s mple inanncr by springing one leg of the magnet ils'cll As the pole pieces are carried (lil'ccll by the legs of the magnet the springing of the magnet legs as described 1 5 above adjusts the gap between the poles ina' simple but ell'cclive way. i

'0 claim:

1. .-\n actuating device for loud speakers t'uliiplisllig a magnet, a U-shaped pole piece, Ito and a strap engaging the pole piece and at least partly encircling a portion of the magnet to attach the pole piece to the magnet.

3. An actuating device for loud speakers comprising a magnet,- a U-shaped pole piece, 123 a clamping device engaging the pole piece and at least partly encircling a portion of the magnetand means associated with the clamping device for retracting the base of said pole piece against the magnet.

3. An actuating device for loud speakers comprising a horseshoe magnet, a U-shaped pole piece associated with each pole of the magnet, means for attaching each pole piece to the corresponding pole of the magnet comprising a clamping device engaging the pole piece and at least partly encircling the polar portion of the ma net, means associated with the clamping evice for retracting the base of the pole piece against the polar portion of the magnet, the two pole pieces in conjunction forming a rectangular coil receiving opening,- coils positioned in said opening, .and an armature extending axially through said coils with each end positioned between a pole of one pole piece and the adjacent pole of the other pole piece.

4. An actuating device for loud speakers comprising a magnet, a U-shaped pole piece and means for clamping the base of the pole piece against a face of the magnet comprising a strap engaging the pole piece and at least partly encircling a portion of the magnet, and a set screw associated with said strap and reacting against a face of the magnet to draw he base of the pole piece against the magnet.

5. An actuating device for loud speakers comprising a magnet, a pole piece, a U- shaped clamping strap the ends of which engage with the pole piece, said clamping strap at least partly encircling a portion of the magnet, and means for causing said clamp ing strap to retract said pole piece against anadjacent face of the magnet.

6. An actuating device for loud speakers comprising a U-shaped magnet, pole pieces associated with the legs of the magnet and extending towards each other and means for adjusting the position of the magnet legs relatively to each other to vary the air gap between the pole pieces said means compris ing a screw secured to one leg of the magnet and extending loosely through the second leg, and a nut on said screw for forcing the second leg of the magnet inwardly toward the first.

7. In an actuating device in accordance with claim (3 an adjustable stop nut on said screw for limiting the inward movement of said second leg of the magnet.

8. An actuating device for loud speakers comprising a U-shaped magnet, a U-shaped pole piece secured to each leg of the magnet, said'pole pieces lying in substantially the sameplane and forming between them a substantially rectangular shaped opening, the corresponding legs of the pole pieces being in alignment and having an air gap between their extremities, speech coils housed within said rectangular opening, an armature fulcrumed intermediate its ends and extending coaxially through said coils,

9. A loud s aker in accordance with claim 8 in whic the speech coils are wound upon spools having side flanges provided with notches, said notches engaging with the bases of the pole pieces to hold the coil spools in place.

10. An actuating device for loud speakers comprising a magnet, a U-shaped pole piece, and a clamping device engaging said pole piece and the external surface of a portion of the magnet for retracting the base of said pole piece against the magnet.

11. An actuating device for loud speakers comprising a magnet having four lateral faces, a pole piece positioned against one of said faces, and a clamping device engaging with said pole piece and having parts which jointly extend around the other three faces of the magnet.

12. An actuating device for loud speakers comprising a magnet having four lateral faces, a pole piece positioned against one of said faces, and clamping means for holding said pole piece in position, said clamping means engaging with the pole piece and having a part reacting against that face of the magnet which is opposite the one against which the pole piece is positioned, all parts of the clamping means being located exteriorly of the faces of the magnet.

13. An actuating device for loud speakers comprising a U-shaped magnet, pole pieces associated with the legs of the magnet and extending towards each other, and means for adjusting the position of the magnet legs relatively to each other to vary the air gap between the pole pieces, said means comprising a rotary member engaging with one of the magnet legs and adapted when turned to adjust said leg toward and away from the other, and an adjustable stop against which said last named leg is adapted to abut. for limiting the approaching movement of the magnet legs and pole pieces, said stop when engaged by the magnet leg serving to prevent further rotation of said rotary member in a direction which would cause further approaching movement of the magnet legs.

14. An actuating device for loud speakers comprising a U-shaped magnet, pole pieces associated with the legs of the magnet and extending towards each other, and means for adjusting the position of the magnet legs relatively to each other to vary the air gap between the pole pieces, said means comprising a screw secured to one leg of the magnet and extending loosely through the second leg, and two nuts on said screw located on opposite sides of said second magnet leg.

15. An actuating device for loud speakers comprising a substantially U-shaped magnet net whereby the distance between the ends of at least oneleg of which may be flexed. a said pole pieces may be varied.

pole piece associated with each leg of the In testimony whereof we affix our signa- 10 magnet, said pole pieces being positioned in tures.

the space between the legs of the magnet and projecting towards each other, and CLAIR L. FARRAND. means for flexing at least one leg of the mag- ERNEST ROSS. 

